The purpose of this project is characterize the cognitive and behavioral circumstances under which neurons in the dorsolateral prefrontal cortex (DLPFC) of the rhesus macaque monkey are active. The general hypothesis to be tested is that neurons of the DLPFC are active under circumstances which behavior must be controlled through the deliberate maintenance of internal states rather than by external stimuli or automatic processes. In four experiments, the activity of single neurons in the DLPFC will be monitored while monkeys perform tasks in which the level of demand placed on endogenous control is systematically manipulated. Manipulated task parameters will include: the number and nature of items held in work memory (experiment 1); the degree to which the stimulus-response associations have become automatized (experiment 2); the degree to which correct responses are opposed by innately prepotent response tendencies (experiment 3); and the degree to which correct responses are opposed by prepotent response tendencies learned in other task contexts (experiment 4). At a general level, the results of these experiments will help to characterize the cognitive functions of DLPFC and will thereby provide a framework for assessing and understanding prefrontal-dependent cognitive functions in normal and schizophrenic human subjects. At a specific level, they will provide insight into the nature of neural events underlying the mass signals detected by functional imaging in human subject will provide insight into the nature of neural events underlying the mass signals detected by functional imaging in human prefrontal cortex (Project-Cohen); and they will open up the possibility of testing in primates the impact of DLPFC of pharmacological and lesion interventions now being developed in rat studies (Projects-Zigmond and -Grace).